The invention relates to a method for fabricating a bond by bonding an electrical contact conductor to a bond partner. The durability of such bonds can be diminished, however, when the metallic surface of the bond partner is altered by an unwanted chemical reaction, for example, oxidation of the metallic surface. Such oxidations can occur, e.g., when the bond partner is exposed to an oxygenated atmosphere for a lengthy period of time and/or high temperatures before the bond is made.
When, for example, a copper contact conductor is bonded to a copper layer whose surface is already oxidized no satisfactory durably effective electrically conductive bond is achieved because its life is shortened. It is particularly when such a bond is exposed to frequent wide-ranging changes in temperature that there is often the problem of the contact conductor becoming detached from the copper layer. However, problems of this kind are not just limited to copper or bond partners and/or contact conductors containing copper.
One way of getting around these problems is to provide the metallic surface of the bond partner with a protective layer of a precious metal to thus prevent oxidation or some other change in the metallic surface to be bonded. This is done by using bond leads in the form of wires likewise made fully or at least mainly of a precious metal. However, it is particularly in the field of power electronics that high amperages are involved necessitating the use of heavy gauge bond leads and/or circuiting numerous bond leads electrically in parallel. Using precious metals for protective layers and bond leads hikes the material costs not just in making bonds in small-signal electronics but even more so in power electronics. There is thus a need for a lower-cost solution.
A further disadvantage of such precious metal protective layers is that they are very soft and—when a contact conductor is bonded to the protected metallization—act as a lubricant, detrimenting the quality of the bond. Apart from this, applying a precious metal protective layer makes for additional work, adding to the expense in fabrication. There is thus a need to avoid the cited disadvantages by an improved method for fabricating a bond.